Method for garbage collection of unused methods

ABSTRACT

The present invention provides a system and a method of improving the effectiveness of a data processing application when using a virtual machine, where the program includes many methods, i.e. program sections, that are stored in the memory of the computer used, and where garbage collecting is used by said program, wherein the method is characterized by a first step in which all thread stacks are analyzed with respect to methods required thereby; a second step in which each of the methods required is caused to be regenerated where occurrent references to a method are replaced with reference to regenerated methods prior to the regeneration of a method; and by a third step in which all non-regenerated methods are erased, wherein the corresponding memory space is placed at the disposal of said program.

CROSS REFERENCE TO RELATED APPLICAITONS

This application is a continuation application of U.S. patent application Ser. No. 10/111,566 entitled METHOD FOR GARBAGE COLLECTION OF UNUSED METHODS, filed on Oct. 31, 2002 (Attorney Docket No. BEAS-01246US2) which claims priority from PCT application PCT/SE00/02096, filed Oct. 27, 2000 which claims priority to Sweden Application No. 9903890-3 filed Oct. 28, 1999, and incorporated herein by reference.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.

FIELD OF THE INVENTION

The invention relates to a method of improving the effectiveness of a data processing application when using a virtual machine, where the program includes many application methods.

BACKGROUND

In a computer system, the ability to control the allocation of memory resources is vital to the successful operation and scalability of the computer system as a whole. Software applications run more efficiently in environments in which steps are taken to proactively manage available memory resources to ensure that only those entities that are currently being used are stored in memory, while little-used entities are cleanly removed. Such memory management techniques have commonly been applied to object management, including the JAVA language, and other object-oriented environments. Many memory management techniques can be designed to be automatic, or to allow a developer control over the allocation. JAVA and other dynamic program languages include an automatic memory management. This means that the programmer need not keep an account of those parts of the memory that are used. The virtual machine carries out a so-called garbage collection from time to time, meaning, in principle, that the virtual machine scans the entire memory and finds which objects have been stored in the memory and which objects the program can no longer address. These parts of the memory are returned for later use.

JAVA also includes methods for so called thread management tools. Thus, JAVA incorporates a system for supporting or simulating the simultaneous processing of two or more programs. The thread management can be divided into two parts. One part concerns the manner in which different threads are structured in a controlled manner. Another part is concerned with which threads shall be run and which threads shall be passive and wait to be run.

However, in order to further increase effectiveness and place occupied memory space at the disposal of the program, it is not sufficient to solely optimize the memory with respect to the objects. Additional mechanisms are required when the program includes many application methods, to better optimize the arrangement of application methods within the memory space.

SUMMARY OF THE INVENTION

The present invention relates to a system and method of improving the effectiveness of a data processing application when using a virtual machine, where the program includes many application methods, i.e. program sections, that are stored in the memory of the computer used, and where garbage collecting is used by said program, wherein the inventive method is characterized by a first step in which all so-called thread stacks are analyzed with respect to application methods required thereby; a second step in which each of the application methods required is caused to be regenerated where occurrent references to a method are replaced with reference to regenerated application methods prior to the regeneration of a method; and by a third step in which all non-regenerated application methods are erased, wherein the corresponding memory space is placed at the disposal of said program.

More specifically, the invention is concerned with increasing the data processing rate in virtual machines, and then particularly with respect to the JAVA program language.

The invention is not restricted to JAVA, but can be applied with many program languages, although the invention is described below primarily with reference to JAVA.

The system and methods provided by the invention are intended for use with adaptive optimization of a program. In adaptive optimization, the program is restructured and different parts of the program are optimized as the program is run. The general problem of increasing data processing capacity resides in the rapid creation of new memory sites, since the longer the program is run, the more memory space is required.

In one embodiment the invention comprises a process for optimizing the distribution of application methods within the memory space of a computer system or virtual machine, comprising the steps of: determining a selection of application methods to be regenerated; creating regenerated application methods, and replacing references to each method with references to the regenerated method; and, erasing all non-regenerated application methods and releasing the memory space occupied by those non-regenerated application methods. The above step of determining includes analyzing thread stacks associated with each method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the placement of a JAVA virtual machine in a typical environment.

FIG. 2 illustrates an example of application methods prior to regeneration.

FIG. 3 illustrates application methods regenerated in accordance with the invention.

DETAILED DESCRIPTION

As described above, JAVA and other dynamic program languages include an automatic memory management. The virtual machine carries out a so-called garbage collection from time to time, meaning, in principle, that the virtual machine scans the entire memory and finds which objects have been stored in the memory and which the program can no longer address. These parts of the memory are returned for later use. JAVA also includes methods for so called thread management tools. In such a system, threads form the core technology upon which applications execute and communicate with the server. Thus, JAVA incorporates a system for supporting or simulating the simultaneous processing of two or more programs.

However, in order to further increase effectiveness and place occupied memory space at the disposal of the program, it is not sufficient to solely optimize the memory with respect to the objects. Additional mechanisms are required when the program includes many application methods, to better optimize the arrangement of application methods within the memory space. The present invention solves this problem.

The present invention thus relates to a method of improving the effectiveness of a data processing application when using a virtual machine, where the program includes many application methods, i.e. program sections, that are stored in the memory of the computer used, and where garbage collecting is used by said program. In one embodiment, the method is characterized by a first step in which all so-called thread stacks are analyzed with respect to application methods required thereby; a second step in which each of the application methods required is caused to be regenerated where occurrent references to a method are replaced with reference to regenerated application methods prior to the regeneration of a method; and by a third step in which all non-regenerated application methods are erased, wherein the corresponding memory space is placed at the disposal of said program.

As used herein the JAVA™, Java Virtual Machine™, JVM™ and Solaris™ are trademarks of Sun Microsystems, Inc. The terms Windows™, Windows NT, and WinNT™ are trademarks of Microsoft Corporation. The term LINUX™ is a trademark of Linus Torvalds.

The present invention will now be described in more detail partly with reference to an exemplifying embodiment of the invention shown on to the accompanying drawing in which like numerals represent features common among the drawings.

FIG. 1 shows that a JAVA virtual machine (JVM) 102 can be used to run different data programs 1, 2, 3 (indicated as 104, 106, 108, respectively), regardless of whether the operative system is, for example, WinNT 110, Linux 112, Solaris 114 or some other type of system. As mentioned above, although JAVA is a very popular program language, the present invention is not restricted to this language but can be applied to all object-oriented and platform-independent corresponding program languages.

The present invention thus relates to a system and method of improving the effectiveness of a data processing application when using a virtual machine, wherein the program includes a large number of application methods, i.e. program sections, that are stored in the memory of the computer used, and wherein a garbage collecting process is used by the program.

It is previously known to garbage collect objects and therewith erase objects that are no longer in current use by thereby placing corresponding memory capacity at the disposal of the system.

In large systems, many methods, i.e. program sections, are used one or a few times, or methods are applied for a short period of time and then left unused.

In the case of JAVA and corresponding programs, new application methods are loaded and old application methods left unused.

Furthermore, adaptive optimization results in the optimization and re-optimization of methods placed in the memory, where old application methods are left unused.

When optimizing lock mechanism selections and garbage collection selection, it is necessary to replace all used application methods that use old mechanisms with new mechanisms.

Generally described, the invention first identifies application methods to be regenerated. According to an embodiment of the invention, all so called thread stacks are analyzed with respect to the application methods required, in a first step of the inventive method. In a second step, each of the application methods required is regenerated, where occurrent references to a method are replaced with references to regenerated application methods prior to said regeneration. In a third step, all non-regenerated application methods are erased and the corresponding memory space placed at the disposal of the program.

This procedure does not only clean out unused application methods, but also results in a reorganization between those application methods that have been regenerated, so as to direct any references to the original application methods immediately to appropriate regenerated application methods instead of proceeding via an old method that is no longer used.

This is illustrated in the example of FIGS. 2 and 3, in which example application methods foo and bar are used for illustration. It will be evident to one skilled in the art that the JAVA-based foo and bar application methods shown in FIGS. 2 and 3 are given for purposes of illustrating the regeneration and garbage collection features of the invention, and that the invention is not limited solely to the types of application methods herein, but can be used with a wide variety of method-based systems.

FIG. 2 illustrates the old or original application methods, and FIG. 3 illustrates the regenerated application methods. Three application methods foo 116, apa 118 and bar 120 are shown in FIG. 2. In the example shown, the foo method 116 starts at the memory address 4711. The apa method 118 starts at the address 4714, and bar method 120 starts at the address 4720.

In this example, analysis of the thread stacks shows that only the application methods foo and bar are used and consequently foo and bar have not been referenced to the method apa.

FIG. 3 illustrates how the application methods foo and bar are regenerated to provide new application methods. In the example illustrated in FIG. 3, the new application methods foo 122 and bar 124 are recreated precisely to match their original predecessors, although with the difference that the new application methods obtain new addresses. In the example shown, the foo reference to bar now points to the new bar address 4903.

All of the old application methods, i.e. the application methods foo 116, apa 118 and bar 120 shown in FIG. 2, can now be erased and the memory spaces previously occupied by these application methods vacated for further use.

When garbage collection of objects takes place, running the program normally stops while garbage collection takes place. Running of the program is restarted subsequent to the garbage collection and to the erasure of objects that are not in use.

Such a method can be used when applying the present invention.

However, the following method is preferable.

When practicing the inventive method, one thread is stopped at a time whilst the program is running, wherewith application methods used for a stopped thread are selectively transferred to a list and the thread then restarted. The application methods in the list are then regenerated and stored. All threads are later caused to be stopped at the same time, subsequent to having treated all threads this way, namely so that all used application methods relating to the threads concerned have been regenerated. All application methods that have not been regenerated are erased and all threads are restarted with the regenerated application methods.

This method obviates the need to stop running the program, since the regeneration takes place intermittently.

As before mentioned, lock mechanisms are used in JAVA and corresponding languages. Different lock mechanisms can be selected. The important thing is to select the lock mechanism that is the most effective in preventing more than one thread having access to a given object at the same time as another thread.

A synchronization problem exists when several threads desire access to one and the same object or source. In order to solve this problem in JAVA, each thread endeavors to reach the source lock. The source lock mechanism can be used in various ways. The effectiveness of different lock mechanisms will depend on how threads endeavor to obtain access to synchronized sources.

According to a preferred embodiment, when locking mechanisms are used the most effective locking mechanisms are identified in a step prior to said first step, and the application methods that use a thus identified locking mechanism are regenerated.

With respect for garbage collecting algorithms, these also need to be selected. Many object oriented languages use garbage collection. This means that the programmer need not instruct the system explicitly that a certain object is no longer required. The system is responsible for this detection, and reclaims the part of the memory occupied by the object. A number of different algorithms have been proposed for effective implementation of this detection and reclaim. It has been found that different algorithms are best for different applications. The choice of the best garbage collecting algorithm for the program application being run is highly significant in achieving maximum execution rate in respect of the program concerned.

According to another preferred embodiment of the invention, when different garbage collecting algorithms are used the allocation and length of life of the various objects are determined in a step prior to said first method step, whereafter the most effective garbage collecting algorithm is caused to be identified and application methods that constituting the requisite garbage collecting algorithms are regenerated and remaining garbage collecting algorithms then erased.

Application of the preferred embodiments provides a highly effective method for optimizing codes, threads and memory management, where a generic feature resides in the identification and regeneration of application methods so as to not load the system with unused application methods.

The foregoing description of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to the practitioner skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalence. 

1. A method of optimizing distribution of software methods within a memory space of a virtual machine, comprising the steps of: determining, within a plurality of methods originally distributed within a memory space of a virtual machine, a selection of the plurality of methods to be regenerated, wherein the step of determining includes stopping each running thread and, while the thread is stopped, determining methods in the stopped thread that are currently required by applications running on the virtual machine; creating regenerated methods corresponding to the methods currently required by applications running on the virtual machine; replacing references to each method in the original selection with references to the regenerated method; restarting the stopped thread; and erasing any other methods that have not been regenerated.
 2. The method of claim 1, wherein the step of analyzing threads includes analyzing thread stacks to determine the methods currently required by the threads.
 3. The method of claim 1, wherein the step of creating regenerated methods includes stopping the threads and recreating at an alternate memory address a copy of the methods required by the threads.
 4. The method of claim 1, wherein the step of erasing includes releasing the portion of memory space occupied by the non-regenerated methods.
 5. The method of claim 1, wherein the step of determining includes determining an optimal locking mechanism to be used with the selection of methods.
 6. The method of claim 1, wherein the step of erasing includes using a stop and copy method of garbage collection.
 7. The method of claim 1, wherein the step of restarting the stopped thread takes place before the step of erasing any other methods that have not been regenerated.
 8. The method of claim 1, wherein the step of restarting the stopped thread takes place after the step of erasing any other methods that have not been regenerated.
 9. A system for optimizing distribution of software methods within a memory space of a virtual machine, comprising: a virtual machine having a memory space and methods stored therein; and a garbage collector that determines, within a plurality of methods originally distributed within a memory space of a virtual machine, a selection of the plurality of methods to be regenerated, wherein the garbage collector stops each running thread and, while the thread is stopped, determines methods in the stopped thread that are currently required by applications running on the virtual machine, creates regenerated methods corresponding to the methods currently required by applications running on the virtual machine, replaces references to each method in the original selection with references to the regenerated method, restarts the stopped thread, and erases any other methods that have not been regenerated.
 10. The system of claim 9, wherein the step of determining the methods currently required includes analyzing thread stacks to determine the methods currently required by threads.
 11. The system of claim 9, wherein the step of creating regenerated methods includes stopping the threads and recreating at an alternate memory address a copy of the methods required by the threads.
 12. The system of claim 9, wherein the step of erasing includes releasing the portion of memory space occupied by the non-regenerated methods.
 13. The system of claim 9, wherein the step of determining includes determining an optimal locking mechanism to be used with the selection of methods.
 14. The system of claim 9, wherein the step of erasing includes using a stop and copy method of garbage collection.
 15. The system of claim 9, wherein the step of restarting the stopped thread takes place before the step of erasing any other methods that have not been regenerated.
 16. The system of claim 9, wherein the step of restarting the stopped thread takes place after the step of erasing any other methods that have not been regenerated.
 17. A computer readable medium including instructions stored therein which when executed by a computer causes the computer to perform the steps of: determining, within a plurality of methods originally distributed within a memory space of a virtual machine, a selection of the plurality of methods to be regenerated, wherein the step of determining includes stopping each running thread and, while the thread is stopped, determining methods in the stopped thread that are currently required by applications running on the virtual machine; creating regenerated methods corresponding to the methods currently required by applications running on the virtual machine; replacing references to each method in the original selection with references to the regenerated method; restarting the stopped thread; and erasing any other methods that have not been regenerated.
 18. The computer readable medium of claim 17, wherein the step of restarting the stopped thread takes place before the step of erasing any other methods that have not been regenerated.
 19. The computer readable medium of claim 17, wherein the step of restarting the stopped thread takes place after the step of erasing any other methods that have not been regenerated. 